Fluorination Strategy\nfor Benzimidazole Core Based\nElectron Acceptors Achieving over 19% Efficiency for Ternary Organic\nSolar Cells

The expansion of two-dimensional conjugated systems in\nnonfullerene\nelectron acceptors (NFAs) has significantly advanced the molecular\ndesign and efficiency potential of organic solar cells (OSCs). This\nstudy introduces a novel class of NFAs featuring a benzimidazole core\nwith varying degrees of peripheral fluorination, designated as YIS-4F,\nYIS-6F, and YIS-8F, respectively. Through systematic modulation of\nfluorine content, we observed that OSCs incorporating YIS-6F achieved\nthe highest power conversion efficiency (PCE) of 17.28%, surpassing\nthose with YIS-4F and YIS-8F. Notably, the incorporation of YIS-6F\nin a ternary blend with D18/N3 yielded a remarkable PCE of 19.43%.\nThe enhanced performance of YIS-6F-based devices is attributed to\nthe optimized energy level alignment and optimized crystallinity,\nwhich collectively facilitate efficient exciton dissociation, accelerated\ncharge transport, and minimized charge recombination, culminating\nin an exceptional fill factor and PCE. Our findings underscore the\npivotal role of fluorination of NFAs at the central benzimidazole\ncore in optimizing molecular packing, and consequently enhancing the\nperformance of OSCs.